Almost all high power and high current semiconductor devices employ some type of protection to prevent excess current from overheating the semiconductor junctions and damaging them. Typically, this protection includes current limiting circuits that limit the amplitude of the current flowing through the semiconductor device. However, in some applications such as Magnetic Resonance Imaging (MRI), high amplitude current pulses are needed that may exceed the maximum current value of a semiconductor device for a brief period of time. These high amplitude pulses are needed to achieve a high signal-to-noise ratio and reduce the length of time a patient is scanned. Typically, these current pulses are shaped such that the RMS value of the current stays below the prohibited value, but in systems in which current limiters are employed, these current pulses can not be used since the current limiters will limit the amplitude of the pulse regardless of the pulse shape. Thus, current pulses having lower amplitudes and longer periods must be used to achieve the desired results, such as the higher signal to noise ratio in a MRI system. Thus, it is not necessarily the amplitude of the current flowing through the semiconductor device that is important in terms of overheating the semiconductor junction, but rather, the junction temperature itself that is important.
Monitoring the junction temperature is difficult however, since the semiconductor junction is very small and is not easily physically accessible. Semiconductor devices do exist that include integral junction temperature sensors, but in general these semiconductor devices are unable to be used at the high currents required in high power applications.
Therefore, it would be desirable for a system to determine the junction temperature of a high current semiconductor devices and other semiconductor devices without the need to make difficult measurements.